Improve the "View this topic in GitLab" note in markdown.md

Problem to solve

The following discussion from !94111 (merged) should be addressed:

• @digitalmoksha started a discussion:

  View this topic in GitLab has always felt a little incomplete to me, because I don't know why I would want to do that (from an infrequent doc reader point of view). Something like View topic fully rendered in GitLab or something feels more clear.

Further details

Proposal

Who can address the issue

Other links/references